This invention generally relates to needle retraction mechanisms. More particularly, this invention relates to needle retraction mechanisms that are used in the medical field. Such needle retraction mechanisms find particular applicability in connection with intravascular catheters, syringes, blood collection tubes and lancets.
Catheters, particularly intravenous (IV) catheters, are used for infusing fluid, such as normal saline solution, various medicaments and total parenteral nutrition, into a patient or withdrawing blood from a patient. Peripheral IV catheters tend to be relatively short, and are on the order of about one and one-half inches in length. The most common type of IV catheter is an over the needle peripheral IV catheter. As its name implies, an over the needle catheter is mounted over an introducer needle having a sharp distal tip. The catheter and the introducer needle are assembled so that the sharp distal tip of the introducer needle extends beyond the distal tip of the catheter with the bevel of the needle facing up away from the patient's skin.
The catheter and introducer needle assembly is inserted at a shallow angle through the patient's skin into a peripheral blood vessel, i.e. a smaller blood vessel that is not connected directly to the heart but is one of the branches of the central blood vessels that is directly connected to the heart. In order to verify proper placement of the assembly in the blood vessel, the clinician confirms that there is flashback of blood in the needle and in a flashback chamber located at the proximal end of the needle in conjunction with the needle hub. Once proper placement is confirmed, the clinician applies pressure to the blood vessel by pressing down on the patient's skin distal to the tip of the needle and the catheter. This finger pressure minimizes further blood flow through the catheter and needle. The clinician advances the catheter into the blood vessel, withdraws the needle, leaving the catheter in place, and attaches a fluid handling device to the catheter hub.
Once the introducer needle is withdrawn from the catheter, it is a "blood contaminated sharp" and must be properly handled. With the recognition by the medical device industry of the risk of transmission of Acquired Immunosuppressive Deficiency Syndrome (AIDS) by blood contaminated sharps, various needle shielding mechanisms have been developed. One type of a needle shielding mechanism uses a substantially hollow handle with an introducer needle movably disposed in the handle. In such a device, the sharp distal tip of the needle may be extended from a hollow handle so the sharp distal tip of the needle is exposed. After the needle has been used to place a catheter into a patient, the needle can be retracted into the handle so that the sharp distal tip of the needle is no longer exposed. Various biasing mechanisms can be used to allow the introducer needle to be retracted into the handle after use. For example, a helical spring, either in compression or tension, could be used to provide the biasing force. Alternatively, an elastic tube could be used to provide the biasing force. In order to minimize the number of parts needed for the device, a vacuum created in the proximal portion of the handle between the proximal wall of the handle and the proximal portion of the needle hub can be used to provide the biasing force to retract the needle into the handle since the proximal end of the needle is typically connected to a needle hub. Typically a latching mechanism is used to temporarily lock the needle hub in the extended position for use with the catheter so the sharp distal tip of the needle is distal of the distal end of the handle.
When a vacuum is used to provide the biasing force, the needle hub includes an elastomeric stopper that engages the sidewalls of the handle. This stopper creates an airtight seal between the portion of the handle proximal of the stopper and the portion of the handle distal of the stopper. One side effect of the use of an elastomeric stopper is that the frictional force between the stopper and the sidewall tends to hold the needle hub in place even when the latch is activated to allow the biasing mechanism to bias the needle hub toward the proximal end of the handle. Such an occurrence is unacceptable where the needle retraction mechanism is designed to withdraw the needle into the handle to prevent accidental needle sticks.